CN114364866B

CN114364866B - Exhaust gas aftertreatment

Info

Publication number: CN114364866B
Application number: CN202080061798.4A
Authority: CN
Inventors: 罗伯特·史泽洛克; 亚历山大·萨斯多夫; 佛罗莱恩·瑞米勒
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2019-07-15
Filing date: 2020-07-15
Publication date: 2024-07-30
Anticipated expiration: 2040-07-15
Also published as: KR20220031654A; EP3999725C0; CN114364866A; DE102019210415A1; EP3999725A1; EP3999725B1; US11619157B2; US20220316383A1; DE102019210415B4; JP2022541213A; WO2021009238A1

Abstract

The invention relates to a method for exhaust gas aftertreatment, characterized by the following steps: a) providing a raw exhaust gas containing nitrogen oxides, b) introducing the raw exhaust gas containing nitrogen oxides into a catalytic evaporator (1), c) introducing a urea solution and a fuel into the catalytic evaporator (1), thereby obtaining a reducing agent, and d) delivering the reducing agent into an exhaust gas aftertreatment system (8). The invention further relates to a device for producing a reducing agent, to a reducing agent produced thereby, and to the use of these subjects.

Description

Exhaust gas aftertreatment

Technical Field

The invention relates to a method for exhaust gas aftertreatment and to a device for producing a reducing agent for exhaust gas aftertreatment.

Background

Exhaust gas aftertreatment refers to the process of purifying combustion gases after they leave the combustion chamber of an internal combustion engine by mechanical, catalytic or chemical means. In order to reduce nitrogen oxides (NOx) with Selective Catalytic Reduction (SCR) technology, catalysts and reducing agents, such as ammonia, are used. For this purpose, an aqueous urea solution is injected from which ammonia is produced by pyrolysis and hydrolysis during further transport through the exhaust pipe. Three-way catalysts can be used for the reduction of hydrocarbons and carbon monoxide.

The effect of catalytic exhaust gas aftertreatment, i.e. conversion or conversion, depends decisively on the operating temperature, among other factors. Virtually no reaction occurs below about 250 ℃. This is why modern vehicles have high emissions of harmful substances even after cold starts. In this operating state, the catalyst has not yet reached the operating temperature and therefore the conversion of the emitted harmful substances is inadequate.

There are some strategies to rapidly increase the exhaust gas temperature. For example, the catalyst may be placed in the exhaust system near the engine. However, at least in the case of a gasoline engine, there is a risk that the temperature becomes too high in other operating states, for example, when the rated power is approached. As temperatures of 1000 c destroy the catalyst. Good conversion and long service life are obtained at 400 to 800 ℃. Alternatively, the exhaust gas temperature may be increased by an electric heater or by post injection in the engine interior and/or exhaust system.

However, these measures have the following effects: further increases in consumption and produces additional emissions after cold start.

Disclosure of Invention

Starting from the prior art, the object of the invention is therefore: a reducing agent for exhaust gas aftertreatment, optionally comprising selective catalytic reduction, is provided, which enables catalytic conversion at lower temperatures.

According to the invention, a method for exhaust gas aftertreatment, in particular for nitrogen oxide removal, is proposed, which is distinguished by the following steps:

a) Providing a raw exhaust gas containing nitrogen oxides,

B) Introducing said raw exhaust gas containing nitrogen oxides into a catalytic evaporator,

C) Introducing urea solution and fuel simultaneously into a catalytic evaporator, thereby obtaining a reducing agent, and

D) The reductant is delivered to an exhaust aftertreatment system.

The process can be used in particular when the exhaust gas contains nitrogen-oxygen compounds. In this regard, controlled systems are contemplated. The controlled system is switched on at the point of the engine integrated characteristic curve at which the exhaust gas contains an increased amount of nitrogen oxides. At other engine integrated characteristic points where small or tolerable amounts of nitrogen oxides are produced by combustion, the system is not effective. If it is not effective, the delivery of air and exhaust gas is stopped.

The raw exhaust gas containing nitrogen oxides may be raw untreated exhaust gas. It may also be a treated raw exhaust gas, which is treated with, for example, a dust filter and/or a diesel oxidation catalyst.

Steps b) and c) may be performed simultaneously. In step d), the reducing agent may be fed directly into the exhaust gas aftertreatment system or by introducing it into an exhaust gas line leading from the engine to the exhaust gas aftertreatment system.

The method according to the invention was developed on the basis of a catalytic evaporation technique known per se, wherein the original exhaust gas of the engine containing nitrogen oxides, liquid fuel and urea solution were used. Heat is generated within the system by the catalytic conversion of fuel in a catalytic evaporator. In this way, the system is substantially independent of the operation of the engine. It is therefore possible that: the reducing agent is produced from the aqueous urea solution independently of the engine operation, in particular the exhaust gas temperature and the exhaust gas mass flow. Furthermore, in the method according to the invention, hydrogen and hydrocarbons, for example acetylene, are produced from the added fuel, which are used as additional reactants, i.e. reducing agents, in a Selective Catalytic Reduction (SCR) system for exhaust gas Aftertreatment (AGN).

The amounts of urea solution and fuel provided are the usual amounts used in the per se known operating modes of the catalytic evaporator.

The raw exhaust gas containing nitrogen oxides which is fed to the catalytic evaporator may be part of the usual engine exhaust gas, i.e. a part may be separated from the engine exhaust gas stream and provided in step a) as raw exhaust gas containing nitrogen oxides which is led to the catalytic evaporator. This division can be achieved by means of flaps or slides in the exhaust gas line, which can be actuated accordingly. The raw exhaust gas can also be led directly from the engine and fed to the catalytic evaporator.

Advantageously, with the method according to the invention: in contrast to the heating of the entire exhaust gas stream according to the prior art, only a small partial stream of the original exhaust gas containing nitrogen oxides needs to be heated. Additional heat is also generated by the conversion of the fuel, which additional heat does not have to be electrically introduced. For catalytic conversion, only the catalyst needs to be heated. The reaction can be controlled by varying the reactant flow.

Catalytic evaporators can be used in the process according to the invention, since they are known per se from the prior art. The expert also knows how to operate them in principle. An example of a catalytic evaporator which can be used in the method according to the invention is described in DE102015120106Al, which is fully referred to in regard to design details and operation.

The catalytic evaporator used in the process according to the invention may have a catalyst, which may be applied to a support, for example. The catalyst-carrying support may be placed in the reaction vessel such that an intermediate space is formed between the inner surface of the reaction vessel and the catalyst surface.

In operation of the catalytic evaporator, for example, liquid fuel may be added to the inside of the reactor wall of the catalytic evaporator, while an oxidant, such as air, is supplied to the catalyst side. A small portion of the fuel oxidizes on the catalyst and the heat generated therein is used to completely vaporize the fuel. Heat transfer is mainly performed by heat radiation from the hot catalyst surface to the fuel surface. The reactor wall on which the fuel is applied is here cooler than the fuel itself. Deposit or crust formation did not occur at all.

The raw exhaust gas containing nitrogen oxides supplied in step a) may contain residual oxygen. If the concentration of residual oxygen in the raw exhaust gas is sufficient, this may be sufficient as an oxidant for the operation of the catalytic evaporator. If the concentration of residual oxygen in the raw exhaust gas containing nitrogen oxides is too low, in one embodiment, the oxidizing agent may be further introduced into the catalytic evaporator in step c). This oxidant is an additional oxidant in the raw exhaust gas in addition to the residual oxygen. Such an oxidizing agent may be oxygen or an oxygen-containing medium, in particular air. The amount of oxidant may be selected such that the usual amount of oxidant in the catalytic evaporator is reached. The air may come from the environment and may be loaded by the turbocharger if necessary.

In one embodiment, the reducing agent formed in step c) has ammonia (NH ₃). In another embodiment, the reducing agent may additionally have H ₂, CO, hydrocarbons such as ethylene, and mixtures thereof.

In one embodiment, by varying the reactant flows of the fuel, urea solution, the raw exhaust gas containing nitrogen oxides and possibly the oxidant, a separate reductant may be provided according to the operating point in the engine integrated characteristic. Providing such a reducing agent in step c) of the method according to the invention increases the mobility of the SCR system, thereby enhancing the reduction of nitrogen oxides in the engine exhaust. This advantage is particularly useful in cold start and other operating points with cold exhaust aftertreatment systems.

In some embodiments, the urea solution used in step c) may be an aqueous urea solution, in particular a 32.5% urea solution. This has proven to be particularly suitable for exhaust gas aftertreatment systems.

In one embodiment, the exhaust gas aftertreatment includes pyrolysis and hydrolysis known per se and selective catalytic reduction also known per se. The reducing agent obtained from the catalytic evaporator may be first subjected to hydrolysis and then to selective catalytic reduction. In another embodiment, the exhaust gas aftertreatment, including the selective catalytic reduction if necessary, may be run at a temperature already 170 ℃ (and possibly higher, e.g. 180 ℃, 190 ℃ or 200 ℃). This means, therefore, that with the method according to the invention, exhaust gas aftertreatment can already be started and carried out at a much lower temperature than is known in the prior art.

The method according to the invention can be used for converting nitrogen oxides for SCR systems of any type of internal combustion engine which is operated with an SCR system in order to reduce NOx emissions.

The subject of the invention is also the use of a catalytic evaporator as described in detail herein in a process according to the invention as also described in detail above.

Furthermore, a reducing agent is provided, which can be obtained by the method according to the invention. Reference is made to the above embodiments with respect to the manner of manufacture and composition. In particular, the reducing agent has hydrogen, hydrocarbons, in particular ethylene, ammonia and/or carbon monoxide.

Furthermore, an apparatus for producing a reducing agent for exhaust gas aftertreatment is described, for example comprising an SCR, wherein the apparatus comprises:

a) The catalytic evaporator is provided with a plurality of air inlets,

B) A raw exhaust gas inlet line to the catalytic evaporator, which is adapted to introduce raw exhaust gas containing nitrogen oxides into the catalytic evaporator,

C1 A fuel inlet line to the catalytic evaporator adapted to introduce fuel into the catalytic evaporator and a urea inlet line to the catalytic evaporator adapted to simultaneously introduce urea solution into the catalytic evaporator; or (b)

C2 A feed line adapted to introduce a mixture comprising urea and fuel into the catalytic evaporator; and

D) A line suitable for introducing the reducing agent produced in the evaporation into the exhaust system of the engine, which leads to an AGN possibly comprising an SCR, or directly into an exhaust gas aftertreatment system, in particular first into a device for hydrolysis and then into a device for selective catalytic reduction.

By the term "adapted" as used hereinabove, it is meant that the respective pipelines are designed such that they can guide the material conveyed therein without negative influence, i.e. such pipelines are inert with respect to the material to be guided, for example. Furthermore, the term "adapted to" also indicates that the corresponding line is connected to a reservoir with the material to be transported.

From the above features cl) and c 2) it is clear that: either urea in the respective solution is added to the catalytic evaporator separately from the fuel (feature cl)), or alternatively (feature c 2)) a mixture of urea solution and fuel is introduced into the catalytic evaporator. In particular in the case where the fuel is miscible with the urea solution, the mixture may be introduced. This relates, for example, to alcohols, such as ethanol, as fuel.

In one embodiment of the device according to the invention, the device may also have an oxidant inlet line to the catalytic evaporator, which is adapted to introduce an oxidant into the catalytic evaporator. Such an oxidant, such as oxygen or air, may need to be fed if the raw exhaust gas does not have the necessary concentration of residual oxygen.

In one embodiment, the exhaust gas aftertreatment comprises a device for hydrolysis and a device for selective catalytic reduction known per se. The apparatus for hydrolysis may for example comprise a hydrolysis catalyst. The device for selective catalytic reduction may, for example, have a catalyst for selective catalytic reduction. The device for hydrolysis and the device for selective catalytic reduction can be arranged in different housings. This can be achieved by: these devices are built independently of each other at different locations of the device according to the invention.

The subject of the invention is also the use of the device as described above for exhaust gas aftertreatment including selective catalytic reduction.

By means of the device described above, the advantages achieved by the method according to the invention can be achieved in a simple and advantageous manner.

Drawings

The invention is explained in more detail below with the aid of the drawing without limiting its general idea. Wherein:

fig. 1 shows a schematic illustration of an embodiment of a device with a catalytic evaporator for exhaust gas aftertreatment;

fig. 2 shows a schematic view of another embodiment of the device according to the invention;

Fig. 3 shows a schematic view of another embodiment of the device according to the invention;

Fig. 4 shows a schematic view of an embodiment of the device according to the invention;

FIG. 5 shows a view of a catalytic evaporator that may be used in an exemplary manner;

fig. 6 shows the operation principle of the catalytic evaporator shown in fig. 2.

Detailed Description

Fig. l shows schematically a device for exhaust gas aftertreatment, which has a catalytic evaporator 1, which is explained in more detail in the following fig. 4 and 5. The engine 9, for example a diesel engine, is used in the usual manner for the operation of a motor vehicle, wherein a fuel supply 10 and an air supply 11 are carried out. The raw exhaust gas produced, which contains nitrogen oxides, is discharged from the engine via line 2. These raw exhaust gases containing nitrogen oxides from the engine 9 are fed to a device 8 for exhaust gas aftertreatment. The exhaust gas aftertreatment 8 has a device 81 for hydrolysis, for example a hydrolysis catalyst, and a device 82 for selective catalytic reduction. The device 81 for hydrolysis and the device for selective catalytic reduction may be present in separate housings. At least a portion of the raw exhaust gas containing nitrogen oxides branches off via line 7 and is fed to catalytic evaporator 1. The urea solution is also fed from a container 13 for urea solution to the catalytic evaporator 1 via the urea inlet line 4. Furthermore, fuel is supplied from the fuel container 12 to the catalytic evaporator 1 via the fuel supply line 3. An oxidant, for example air, can be fed to the catalytic evaporator 1 via an oxidant feed line 5. The reducing agent, which may include in particular NH ₃、H₂, hydrocarbons and CO, is produced in the catalytic evaporator 1 and is introduced into the exhaust system of the engine 9 via the line 6.

Fig. 2 schematically shows a further embodiment of the device according to the invention, wherein identical components of fig. 1 have the same reference numerals, and reference is therefore made to fig. 1 in terms of constructional design and manner of operation. As shown in fig. 2, a mixture of urea and fuel is produced in the chamber 131 and this mixture is then introduced into the catalytic evaporator 1 via the inlet line 41. The prior mixing of urea and fuel may be used with a fuel that is miscible with water, such as an alcohol, e.g., ethanol.

Fig. 3 schematically shows a further embodiment of the device according to the invention, wherein identical components of fig. 1 and 2 have the same reference numerals, and reference is therefore made to fig. 1 and 2 in terms of constructional design and manner of operation. In the apparatus of fig. 3, the reducing agent obtained from the catalytic evaporator 1 is first introduced into the apparatus 81 for hydrolysis. The material resulting therefrom is then introduced into the exhaust system and is then forwarded to the device 82 for selective catalytic reduction.

Fig. 4 shows another embodiment of the present invention. Which corresponds to the plant shown in fig. 3, in which a mixture of urea and fuel is produced in a chamber 131, which mixture is then introduced into the catalytic evaporator 1 via an inlet line 41.

Fig. 5 shows a catalytic evaporator 1, which is used in the method according to the invention. The catalytic evaporator 1 has a catalyst 112 which is applied to a metal mesh 113. As the catalyst 112 and the metal mesh 113, such materials known in the art can be used herein. A metal mesh 113 with catalyst 112 may be present in the reaction vessel 114. In fig. 5, the following is shown for clarity: the catalyst 112 is pulled out of the reaction vessel 114 together with the metal mesh 113. If the catalyst 112 is inserted into the reaction vessel together with the metal mesh 113, an intermediate gap is formed between the inner surface 115 of the reaction vessel 114 and the surface of the catalyst 112 on the metal mesh 113.

Fig. 6 schematically illustrates the operation of the catalytic evaporator shown in fig. 2. Fuel is added to the lower surface of the reaction vessel 114, while raw exhaust gas containing nitrogen oxides and if necessary further oxidant are transported to the catalyst side. A small portion of the fuel is oxidized at the catalyst 112 and the heat generated therein is used to fully vaporize the fuel. The heat transfer is mainly performed by heat radiation from the hot surface of the catalyst 112 onto the surface of the fuel film. The walls of the reaction vessel 114 coated with fuel may be cooler than the fuel itself. Thus no deposit or crust formation at all.

Of course, the invention is not limited to the embodiments shown in the figures. Accordingly, the foregoing description is not to be considered as limiting, but rather as explanatory. The following claims should be construed to: the features mentioned are present in at least one embodiment of the invention. This does not preclude the presence of further features. If the description or claims define "first" and "second" features, this helps to distinguish similar features from each other without specifying a priority.

Claims

1. A method for exhaust gas aftertreatment, comprising at least the steps of:

a) Providing a raw exhaust gas comprising nitrogen oxides;

b) Introducing the raw exhaust gas containing nitrogen oxides into a catalytic evaporator;

c) Introducing urea solution and fuel simultaneously into the catalytic evaporator, thereby obtaining a reducing agent, and

D) The reductant is delivered to an exhaust aftertreatment system,

Wherein the individual reducing agents are provided by varying the reactant flows of the fuel, urea solution, raw exhaust gas containing nitrogen oxides and depending on the operating point in the engine integrated characteristic.

2. The process according to claim 1, wherein, in addition, in step c), an oxidizing agent is introduced into the catalytic evaporator.

3. The method of claim 1 or 2, wherein the reducing agent has ammonia.

4. The method of claim 1, wherein the reductant has any one of hydrogen, carbon monoxide, and hydrocarbons.

5. The method of claim 1, wherein the urea solution is a 32.5% urea solution.

6. The method according to claim 1, wherein the composition of the reducing agent is adjusted by introducing the urea solution, the fuel, the raw exhaust gas containing nitrogen oxides and/or an oxidizing agent.

7. The method of claim 1, wherein the exhaust aftertreatment includes pyrolysis and hydrolysis and selective catalytic reduction.

8. The method of claim 1, wherein the exhaust aftertreatment is operable at a temperature of 170 ℃ or greater.

9. An apparatus for manufacturing a reducing agent for exhaust aftertreatment, wherein the apparatus comprises:

a) A catalytic evaporator;

b) A raw exhaust gas input line to the catalytic evaporator, the raw exhaust gas input line being adapted to introduce raw exhaust gas containing nitrogen oxides into the catalytic evaporator;

c1 A fuel inlet line to the catalytic evaporator and a urea inlet line to the catalytic evaporator, the fuel inlet line being adapted to introduce fuel into the catalytic evaporator, the urea inlet line being adapted to simultaneously introduce urea solution into the catalytic evaporator;

d) A line arranged to introduce the generated reductant into an exhaust system of the engine,

10. An apparatus for manufacturing a reducing agent for exhaust aftertreatment, wherein the apparatus comprises:

a) A catalytic evaporator;

d) A line arranged to introduce the generated reducing agent into the exhaust gas aftertreatment system,

11. An apparatus for manufacturing a reducing agent for exhaust aftertreatment, wherein the apparatus comprises:

a) A catalytic evaporator;

c2 A feed line adapted to introduce a mixture comprising urea and fuel into the catalytic evaporator;

12. An apparatus for manufacturing a reducing agent for exhaust aftertreatment, wherein the apparatus comprises:

a) A catalytic evaporator;

13. The apparatus according to any one of claims 9 to 12, wherein the apparatus further has an oxidant input line to the catalytic evaporator, the oxidant input line being adapted to introduce an oxidant into the catalytic evaporator.

14. The apparatus of any one of claims 9 to 12, wherein the exhaust aftertreatment system comprises an apparatus for hydrolysis and an apparatus for selective catalytic reduction.